RESISTIVE SOLDERING OF LINE N 6 ka BUS BARS IN THE DISPERSION SUPRESSOR ZONE

Transcription

1 CERN CH-1211 Geneva 23 Switzerland the Large Hadron Collider project LHC Project Document No. CERN Div./Group or Supplier/Contractor Document No. AT-CRI-CI/TC/cl EDMS Document No Date: Installation Procedure RESISTIVE SOLDERING OF LINE N 6 ka BUS BARS IN THE DISPERSION SUPRESSOR ZONE Abstract Some of the LHC Dispersion Suppressor (DS) interconnections are housing the 6 ka splices, located in line N in order to power specific quadrupole magnets. In order to respect the thermodynamic budget of the LHC machine the electrical resistance at 1.9K shall be lower than 1.5nOhms. Since 261 splices have to be carried out in the LHC machine, a reliable joining technique has to be applied. This Engineering Specification describes the technology chosen and the requirements imposed on the connections of 6 ka bus bars. Prepared by: Thierry Colombet AT/CRI Checked by: Jean-Philippe Tock Approved by: Alain Poncet Approval and Distribution lists: LHC Interconnections: M. Bajko, D. Bozzini, J. Casas-Cubillos, P. Cruikshank, K. Dahlerup- Petersen, L. Evans, C. Garion, M. Genet, C. Hauviller, R. Herzog, A. Jacquemod, K. Kershaw, F. Laurent, Ph. Lebrun, P. Lepeule, E. Manola, S. Marque, S. Mathot, K-H. Mess D. Missiaen, R. Ostojic, V. Parma, A. Perin, J-L. Perinet-Marque, L. Perrollaz, A. Poncet, P. Proudlock, F. Rodriguez-Mateos, P. Rohmig, L. Rossi, E. Roy, S. Russenschuck, R. Saban, G. Schneider, N. Siegel, A. Siemko, F. Simon, B. Skoczen, P. Strubin, L. Tavian, J-Ph. Tock, D. Tommasini, Th. Tortschanoff, R. Trant, R. Veness, A. Vidal, J. Vlogaert, L. Walckiers, R. van Weelderen, W. Weingarten, L.R. Williams.

2 Page 2 of 25 History of Changes Rev. No. Date Pages Description of Changes draft All LHC-DC-ES rev. 0.1-draft: First draft prepared by Frédérique Schauf, sent for checking and approval to the above distribution list. Deadline 21 October All LHC-QBQID-ES rev. 1.0: Change of LHC Project Number (from LHC-DC-ES-0005 to LHC-QBQID-ES-0001) + minor modifications + addition of drawings. Document released All Version 1.1: correction of a typing error. Version 1.1 released All Version 1.2-draft sent for approval to the above lists. Deadline: 17 February All Minor modications included after approval circuit. Version 2.0 released All Version 2: prepared by Thierry Colombet. Major modifications.

3 Page 3 of 25 Table of Contents 1. INTRODUCTION CHOICE OF TECHNOLOGY RESISTIVE SOLDERING PRINCIPLE RESISTIVE SOLDERING OF THE 6 KA BUS BAR DISPERSION SUPPRESSOR ZONE: DS SUBSECTOR: CONNECTION BOX: PREPARATION OF THE EXTREMITIES TOOLS NEEDED: PREPARATION PROCEDURE INSERTION OF THE 6 KA BUS BAR IN THE LINE N RESISTIVE SOLDERING OF THE 6KA BUS BAR RESISTIVE SOLDERING DEVICE (PORTABLE OVEN) THE OVEN SYSTEM TOOLS NEEDED SOLDERING PROCEDURE SPECIAL CASE OF SOLDERING CONNECTION BOX WITH 12 OR 9 JUNCTIONS LIST OF DRAWINGS REFERENCE...25

4 Page 4 of INTRODUCTION Some of the LHC Dispersion Suppressor (DS) interconnections are housing the 6 ka splices, located in line N in order to power specific quadrupole magnets. In order to respect the thermodynamic budget of the LHC machine the electrical resistance at 1.9K shall be lower than 1.5nOhms. Since 261 splices have to be carried out in the LHC machine, a reliable joining technique has to be applied. This Engineering Specification describes the technology chosen and the requirements imposed on the connections of 6 ka bus bars. 2. CHOICE OF TECHNOLOGY The 6 ka bus bars of line N are made of 13 superconducting strands and 7 copper strands (figure 1). These bus bars cross the dispersion suppressor (DS) zones and have to be connected from the Distribution Feed Box (DFB) to the magnets (261 splices in the LHC machine). Cupper strands Superconducting strands Figure 1-6KA strands Several methods had been envisaged and tested for the joints: inductive soldering, resistive soldering, ultrasonic welding. The points to check for each method were: electrical resistance of splice at 1.9 K lower than the maximum specified (1.5 nω). mechanical cohesion between strands inside the splice. conservation of the copper cross section. repeatability and reliability of the method above specified parameters. the possibility of applying the joining method in a limited space limitation conditions. Cost Intervention time

5 Page 5 of 25 The technology of ultrasonic welding turns out to be non-applicable in this case, as the high pressure needed to assure the cohesion between strands damages the superconducting strands. The resistive soldering has been chosen, as it permits to respect the electrical and mechanical requirements, with a good repeatability and reliability. It has been estimated more applicable than inductive soldering for the simplicity of tooling, considering the relative low number of splices to carry out. Its main advantage is a compactness of the tool that allows to the work in a very confined space. 3. RESISTIVE SOLDERING 3.1 PRINCIPLE Resistive soldering consists in heating the bus bars extremities under pressure in a specific oven with solder. Flux is also used to remove the metal oxides and to make the solder grip to the copper. Before any operation, the bus bar extremities have to be prepared as explained in chapter 5. This process can be divided on several stages: 1. Preparation of the bus bar extremities (both sides). 2. Insertion of the 6KA bus bar into the DS zone. 3. Installation of the oven with flux, copper casing and solder layer and application of pressure. 4. Heating of the assembly. 5. Volatile evaporation, flux concentration and flux activation. 6. Solder melting. 7. Stopping of the heating. 8. Solder solidification. 9. Removal of the oven. 10. Visual check of the joints. 11. Installation of the insulation. 12. Final visual inspection. This engineering specification will follow these stages, detailing some of them. The soldering material used for the 6 ka bus bars splices is Sn96Ag4. The soldering flux (Kester 135) used belongs to the class of EN (see ref [1]) 3.2 RESISTIVE SOLDERING OF THE 6 KA BUS BAR The joint has to ensure the electrical continuity between superconducting strands and between copper strands at respectively cryogenic temperature and during a quench. Several solutions had been studied with the criteria of repeatability, reliability, electrical and mechanical resistance and facilities to execute. The chosen solution consists in preparing the cable into one flat extremity to solder. That involves preparing the extremities in two blades then solders these two blades together (see figure 2).

6 Page 6 of 25 Cupper strands Superconducting strands Figure 2 - soldering principle. 4. DISPERSION SUPPRESSOR ZONE: The DS zone is the zone in the LHC where the beams are focused by magnetic force before the experiments. The main difference with other zone is that in order to perform this focusing, 6KA powering has to be brought to the special Short Straight Section (SSS) in addition to the usual electric cable from the Distribution Feed Box (DFB). 4.1 DS SUBSECTOR: In the figure 3 to 5 two types of subsector are shown (from the drawing [1]) : Figure 3 - Subsector Point 8 left Figure 4 - Subsector Point 8 right

7 Page 7 of 25 Figure 5 - Caption The DS zone is composed of 8 dipoles (blue), 5 SSS (green), 1 connection cryostat and DFBA (dark blue). A DS zone is almost 180m long. The reference [1], [2], [3], [4] respectively described cryomagnet, SSS, connection cryostat and DFBA. 4.2 CONNECTION BOX: There are 8 different types of line N connection boxes in the DS zone: _ 13 connection boxes: 600 A line N connection box (drawing [7]) _ 10 connection boxes: 12 junctions between 6KA bus bar (drawing [8]) _ 2 connection boxes: 9 junctions between 6KA bus bar (drawing [9]) _ 5 connection boxes: 3 junctions between 6KA bus bar, three 6KA bus bar going through and the 600 A cable (drawing [10]) _ 12 connection boxes: 3 junctions between 6KA bus bar, two 6KA bus bar going through and the 600 A cable (drawing [11]) _ 12 connection boxes: 3 junctions between 6KA bus bar, one 6KA bus bar going through and the 600 A cable (drawing [12]) _ 12 connection boxes: 3 junctions between 6KA bus bar and the 600 A cable (drawing [13]) _ 32 connection boxes: 600 A line N connection box and the line N plug (drawing [14]) Considering all the connection boxes, there are: (10*12+2*9+5*3+12*3+12*3+12*3)=261 junctions between 6KA bus bar.

8 Page 8 of PREPARATION OF THE EXTREMITIES As already mentioned, in order to get good results on the point of view of the electrical resistance and reliability, a flat solder method has been chosen. This method involves preparation of the cables (see figure 6). Attention, the quality of the final junction depends essentially on the extremities preparations. 80 mm Figure 6 Prepared extremities before soldering between the couple of blades 5.1 TOOLS NEEDED: T1 T2 _ Generator and heating resistance _ The oven and pressure tools See chapter 7.1 T3 _ Flat nose plier SCEM: T4 _ Cutting plier SCEM: T5 _ Two modified Kant twist SCEM:

9 Page 9 of 25 T6 _ Shears SCEM: T7 _ Scissor SCEM: T8 T9 T10 _ Cutter SCEM: _ Metallic Brush SCEM: _ Flux (Kester 135) with a brush SCEM: T11 _ Soldering station SCEM: T12 _ Protection gloves In order to perform this preparation you will also need: _ Solder layer Sn96Ag4 0.4*10mm in ribbon _ Soldering Flux (Kester 135) _ Polyimide (Kapton) tape (SCEM: )

10 Page 10 of PREPARATION PROCEDURE This procedure has been defined with the help of Jean-Michel Hubert (AT/CRI/CI). The following explanation has to be followed strictly. 1. Cut the cable 25mm longer than the final length (T6). The extremities of the cables have to be at 180 +/- 2 mm from the flange. 2. Move the steel protection by sliding it on at least 180 mm, and stick it with kapton tape or pre-preg. 3. Put the kapton tape (here in yellow) on the three cables at 90 mm from the tip. This kapton tape will prevent the cable from stripping itself. The process following has to be done for each cable. 4. Strip it by using the cutter (T8). There are two opposite layers of insulation. Figure 7 - first insulation stripped Figure 8 - Second insulation stripped 5. Identify and separate the strands 90 mm Figure 9 - Stripped cable

11 Page 11 of 25 Figure 10 - Identified strands The superconducting strands are on the circumference and the copper strands around in the centre. The superconducting strands are much stiffer, less brilliant and smaller then the cupper strand. Copper strands 6. Sort the strands on two groups and try to put in straight line the copper strand. _ One with 7 superconducting Superconducting strands and 3 copper strands, strands _ The other with 6 superconducting strands and 4 copper strands. 7. By hand, place the strands of the first group as shown on the figure : Copper strand Superconducting strand Figure 11 - first group of strand position. 8. Using the flat nose plier (T3) pre-place the strands inside it and then use the two modified Kant twist (5) in order to tight them. Push these kant twist at almost 20 mm from each other. Figure 12 Kant twist positioning

12 Page 12 of Put the protection glove (T12) and then with the paint brush (T10), put some flux between the two modified kant twist. 10. Pre-solder the strands together between the kant twist using the soldering iron (T11) with solder layer. Then redo the same operation by displacing the kant twist. Figure 13 First solder operation 11. By slightly displacing the two kant twist and then repeat the pre-soldering of the strand, you will obtain the results shown on the figure 14. Figure 14 After having soldering the first group of strand. Pre-stabilize the strands just ensures their cohesion before the stabilization. The strands must be parallel and shall not cross each others.

13 12. By hand, place the strands of the second group as shown on the figure : Page 13 of 25 Copper strand Superconducting strand Figure 15 - Second group of strand position. 13. Pre-stabilized the second group of strands like the first one. 14. Brush the extremities with a metallic brush (T9) in order to remove the flux. 15. Cut with the scissor (T7) three solder layers that correspond to the length of the oven (70mm) and to the width of the pre-soldered cable (9mm) and put them as shown on figure 16. Solder layer Figure 16 Before soldering. 16. Put the prepared extremities in the oven. 5 mm of pre stabilized cable has to got out from the tip of the oven. 17. Bringing into pressure of the oven by screw up the upper part. Figure 17 Prepared cable in the oven

14 Page 14 of Switch on the oven. The temperature increase until 226 C and is stabilized between 226 C and 230 C during 15 second. 19. Stop the heating. 20. Place the brands that go out from the oven using the flat nose pliers. The final prepared length has to be as long as possible. 21. Wait until the temperature is lower than 100 C. 22. Extract the cable from the oven and check the result by visual inspection. Solder must be present between each strand and equally spread. 23. Brush the extremity with a metallic brush (T9) in order to remove the flux. 6. INSERTION OF THE 6 KA BUS BAR IN THE LINE N After the 6KA Bus Bar preparation, the cables have to be inserted in the line N in the tunnel. This installation is explained in reference [2]. 7. RESISTIVE SOLDERING OF THE 6KA BUS BAR 7.1 RESISTIVE SOLDERING DEVICE (PORTABLE OVEN) The resistive soldering installation consists of an oven equipped with a heating resistance powered by a generator. The cables to be joined are situated in the oven. The temperature must be controlled in real time to avoid degrading the superconductive properties (see figure 18). That s why a temperature sensor has to be placed as closed as possible from the soldering zone. A pressure has to be applied to the oven. To ensure a repeatable quality of the soldered joints, the pressure shall be kept within the range (10±0.5) MPa for each splice. Oven Electrical resistance generator Temperature sensor PC controlled Data acquisition Figure 18 - Resistive soldering system synoptic

15 Page 15 of THE OVEN SYSTEM The oven has to respect these characteristics: _ usefull length of 70 mm _ temperature closed loop control system (sensor, data acquisition) _ pressure of 10 MPa (+/- 1) during all the soldering process _ can be hold with no danger of burn _ be as small as possible in order to be used in a confined space (connection box) The solution is shown in figure 19 : M6*40 One washer Φ6.2 Upper part of the oven 6* spring washers Φ8.2 M6*20 M5*16 Temperature sensor Mobile part of the oven handle Heating resistance Lower part of the oven Figure 19 - Oven system The characteristics of the heating resistance are: ø8*70mm, 250 W.

16 Page 16 of TOOLS NEEDED T1 T2 T14 T15 T16 T3 _ Generator and the heating resistance _ The oven and the pressure tools See chapter 7.1 _ Protection plate system. _ cupper sheet for 6KA connection _ 10mm wrench. _ Flat nose plier SCEM: T7 _ Scissor SCEM: T10 T11 _ Metallic Brush SCEM: _ Flux with a brush SCEM: T13 _ protection gloves In order to perform this preparation you will also need: _ solder layer Sn96Ag4 0.4*10mm in ribbon and in wire. _ soldering Flux (Kester) _ Polyimide (Kapton) tape (scem: ) _ Glass fiber ribbon. _ Kapton tube

17 Page 17 of SOLDERING PROCEDURE 1. Check that the cables are well positioned and numbered (ask an inspector) and check the suitable length is available in order to realised the junction (between 75 and 70mm of overlapping). 2. Set up the support parts on the two flanges. Support parts Figure 21 Support parts. 3. Pre-place one by one all the cable by slightly bending them and by using the foreseen small part (attention, the 6KA cable must not be bend with a radius higher than 100mm). Small parts Figure 22 - One cable in place on the support. 4. Check the two cables to solder first and carefully remove the 4 closed cables in order not to be disturbed. The two flat extremities have to be in the same direction. 5. Prepare three solder ribbons of dimension: 75mm*10mm*0.4.

18 Page 18 of Prepare one pre-bent copper sheet. 7. Put some flux on the cable and then place the solder ribbons and the copper sheet as shown on the following picture. Solder layer copper sheet Figure 23- Junction assembly Figure 24 Junction assembly 8. Press the assembly with the flat nose pliers T3. Figure 25 - Pressed junction assembly

19 Page 19 of Put the junction on the oven as shown. Do not forget to put the resistance inside. Figure 26 Junction positioning 10. Install the upper part of the oven. Begin to screw up the fourth upper screw until the washer begins to flat. Then screw up the side screws and finally finish to screwing up the first four until the washers are totally flat. Figure 27 - Oven in position 11. Put in place the alimentation and the temperature sensor. 12. Put a fumes extraction system as close as possible from the oven. 13. Check the assembly and the cable to interconnect. 14. Put a cotton rag under the oven, so that the liquefy solder to not leak on other prepared cables 15. Switch on the oven power supply. 16. Temperature increase until 226 C. During the solder liquefying check that the washers always press the junction. 17. Temperature stabilization between 226 C and 230 C during 15 seconds. 18. Stop the heating and wait until the temperature is lower than 100 C. 19. Create an.xls files containing the record of the temperature during the soldering operation. 20. Check that the washers always press the junction.

20 Page 20 of Open the oven by unscrew the 6 screws. Take care not to burn you (remove the mobile parts in order to remove the splice). Figure 28 removing of the splice 22. Brush the splice in order to remove burnt flux. 23. Check the final result by a visual inspection (solder must go out from the copper sheet). 24. Remove the junction from the support. 25. Pre-place the next 2 cables to solder in the support and remove 2 closed cables. Redo the soldering. 26. Redo theses operations until all the cables are interconnected. 27. Ask an inspector to check all the junctions when they are all done. 28. Insulate all the junctions with one non-sticking kapton layer with 50% of overlapping, then with an other kapton layer on the opposite direction still with 50% of overlapping, and at last a layer of pre-preg layer of glass fibber. 1rst : non-sticking Kapton 2 nd : non-sticking Kapton 3rd : pre-preg layer 30 mm 30 mm 130 mm 50% overlapping Figure 29 Insulation scheme. 29. Ask an inspector to check the splice when all the insulations are done.

21 Page 21 of SPECIAL CASE OF SOLDERING In some case in the DS zone, the two cables to solder come from the same side as shown in the figure 30. Figure 30 - Special case. In that case, all the process of soldering is the same, except for the supporting system and for the insulation where it is quite more complicated. Figure 31 soldered special junction

22 Page 22 of 25 Soldered splice 20 mm Put two kaptons layers as explain in but continuing by 20mm after the tip Bending of the Kapton extremity Putting of the preg-pre layer Figure 32 Insulated process of special junction

23 7.6 CONNECTION BOX WITH 12 OR 9 JUNCTIONS LHC Project Document No. Page 23 of 25 Within the DS zone, 10 connection boxes contain 12 or 9 junctions of 6kA cable. The high number of junctions involves carefulness to perform them without problem. On the following figure the cables are shown only in one side to be as clear as possible. Figure junctions connection All the junctions have to be executed carefully. After the last junction, re-place all the junctions on the support parts and screw up the 6 hexagon nuts that keep tight the cable.

24 Page 24 of CONNECTION BOX WITH SPECIAL JUNCTIONS Within the DS zone, 23 connection boxes contain special junctions of 6kA cable. Figure 34 Connexion box with special junction. In this case, glass fiber has to be put on the assembly after the soldering. The glass fibers has to maintain the junction on the pass-through cable and has to be put only on the middle on the junction (between 15 mm and 25mm of glass fiber). Figure 35 Maintaining principle

25 Page 25 of 25 List of drawings [1] LHCQBQID0004 SSS-DFBA INTERCONNECTION (Q7-DFBA) CONNECTION BOX 6 KA [2] In Work [3] In Work [4] In Work [5] In Work [6] In Work [7] In Work [8] In Work [9] LHCQBQID005 MB-SSS INTERCO. ZONE DS(MB-Q9) CONNECTION BOX(600 A, 6 KA) 8. REFERENCE [1] LHC-DC-ES-0003 Soldering flux applied to main bus-bar cables of the LHC [2] In Work